1. Field of the Invention
This invention relates to an excitation circuit for an electronic flash device for a photographic camera, and more particularly to an exciting circuit for an electronic flash device which is particularly suitable for use with a photographic camera having a focal-plane shutter.
2. Description of the Prior Art
In conventional electronic flash devices, the excitation circuit has been arranged to operate the flashtube at its full power once for one shot. Generally, the maximum amount of light which can be emitted from the flashtube is limited according to the size of the flashtube. That is, the maximum light emissive power of the flashtube is determined according to the temperature of the flashtube which depends upon the balance of heat produced by infrared rays included in the emission of the flashtube with the heat dissipation from the flashtube to the atmosphere and to the elements supporting it. Because the flashtube must be operated within a certain working temperature range which is determined taking into account the deterioration rate and breakage of the flashtube, the maximum light emissive power of larger flashtubes having a larger contact area with the atmosphere is inherently larger than that of the smaller ones.
Thus, an attempt to miniaturize the electronic flash device to build it in the camera body encounters a problem that sufficient amount of light cannot be emitted from a small flashtube. However, since the flashtube shares the majority of the overall size of the electronic flash device, the flashtube must be small in order to miniaturize the electronic flash device.
Further, as is well known, the electronic flashtube to be built in a photographic camera having a focal plane shutter is desired to have an emission characteristics curve having a long durable flat peak.